This invention relates generally to vibration absorbers and relates, more particularly, to means for absorbing vibrations, such as bending and torsional vibrations, in a rotating shaft and for reducing speed variations in a rotating shaft.
Shafts which are drivingly rotated commonly experience disturbances during rotation, and these disturbances induce bending and torsional vibrations in the shaft. In an internal combustion engine, for example, the engine crankshaft is exposed to cyclic disturbances in the form of power pulses which tend to excite the crankshaft in both a bending and torsional manner. As another example, in a multi-blade grinding apparatus having rotating blades which are driven by a drive shaft, the drive shaft is exposed to cyclic disturbances which can generate bending and torsional vibrations.
The vibration-inducing disturbances with which this invention is concerned include those which are substantially evenly or regularly-spaced throughout rotation of the shaft. In a multi-cylinder internal combustion engine, for example, these torsional disturbances are a consequence of equally-spaced power pulses generated within the engine cylinders. For example, in an eight-cylinder, four-cycle engine, there are generated four equally-spaced power pulses, and thus four regularly-spaced disturbances for each revolution of the crankshaft. In a multi-blade grinding apparatus, e.g., a tree chopper, having shaft-driven blades which engage objects being ground at a predetermined number of equally-spaced intervals during a single revolution of the driving shaft, there are produced an equal number of regularly-spaced disturbances for each revolution of the shaft. Thus, this invention can be applied to the drivingly-rotated shaft of any internal combustion engine, e.g. a two or four cycle, diesel or spark-ignited, or machine within which are generated evenly-spaced powered strokes or disturbances.
With regard to engine-driven shafts, it is known that vibrations, i.e. torsional vibrations, induced in rotating shafts can be controlled, to a degree, with vibration absorber devices intended to oppose the forces which excite, and thus absorb, the vibrations. The operating principles of a vibration absorber are in contrast to those of a vibration damper which is intended to dissipate energy of the vibrations.
The named inventor of the instant application has described one torsional vibration absorbing system in his U.S. Pat. No. 5,295,411 as including a body attachable to a rotating shaft for rotation therewith and cylindrical rolling elements positioned within cavities disposed within the body. During operation of the system, the torsional disturbances induce pendulum-like motion of the cylindrical elements within the cavities in a manner which absorbs torsional vibration of the shaft. The cylindrical elements, the cavities and the torsional disturbances are related to one another in accordance with an equation which optimizes performance of the system and circumvents time-consuming trial and error techniques during design of the system. While the system of the referenced patent is effective for its intended purpose, it is limited to the absorbing of torsional vibrations, rather than bonding vibrations.
It is an object of the present invention to provide a new and improved system for absorbing vibrations, such as bending and torsional vibrations, in a rotating shaft exposed to disturbances of the aforedescribed class and for decreasing the bending and torsional stresses in, for increasing the stiffness of, and for reducing the noise of such a rotating shaft.
Another object of the present invention is to provide such a system which absorbs bending and/or torsional vibrations and reduces speed variations in a rotating shaft at all shaft speeds.
Still another object of the present invention is to provide such a system whose design can be optimized without the need for time-consuming trial and error techniques.
Yet another object of the present invention is to provide such a system which is uncomplicated in construction and effective in operation.